chromium/third_party/blink/web_tests/external/wpt/css/css-scoping/shadow-reassign-dynamic-004.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Scoping: Dynamic reassignment of a slot.</title>
<link rel="author" title="Edgar Chen" href="mailto:[email protected]">
<link rel="help" href="https://drafts.csswg.org/css-scoping/#selectors-data-model">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1548848">
<link rel="match" href="reference/green-box.html"/>
<div id="host">
  <div id="green" style="background: green"></div>
<div>
<script>
  let root = host.attachShadow({mode: 'open'});
  root.innerHTML = `
    <style>::slotted(div),div { width: 100px; height: 100px }</style>
    <p>Test passes if you see a single 100px by 100px green box below.</p>
    <slot id="slot"></slot>
    <slot>
      <div style="background: red"></div>
    </slot>
  `;

  onload = function () {
    root.offsetTop; // Update layout
    root.getElementById('slot').remove();
  };
</script>